The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Power line communications (PLC) systems transmit and receive signals from a utility to homes over existing power lines in the homes. PLC systems have been used to provide connectivity between a utility and power meters, appliances and other devices located in the homes of consumers. Some of the challenges to the implementation of PLC systems include the relatively noisy environment of the power lines, implementation costs, and transmitting and receiving signals across a transformer.
Channel access may be implemented using Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). Additional background relating to CSMA-CA can be found in IEEE 802.15.4:2006, IEEE Standard for Information Technology—Telecommunications and Information Exchange Between Systems—Local and Metropolitan Area Networks—Specific Requirements—Part 15.4: Wireless Medium Access (MAC) and Physical Layer (physical layer) Specifications for Low-Rate Wireless Personal Area Networks (WPANs).
A random backoff period is used to spread the time during which PLC devices attempt to transmit, which reduces the probability of collisions. Each time that a PLC device attempts to transmit data frames, the PLC device waits the random backoff period. If the channel is idle after the random backoff period, the PLC device transmits the data. If the channel is busy after the random backoff period, the PLC device waits another random backoff period before attempting to access the channel again.
In large power line communication systems, an estimate of channel traffic may be used to avoid excessive collisions when conducting frequent transmission attempts while the chance of success is very low. For example, when a node is trying to associate and join a network, the node sends a data request. All of the nodes in the network that receive the request respond with a response. If the network is busy, there is a high probability that many of the requests or data frames will collide with other packets and corrupt the other packets. The joining node may not receive any detectable response and will try again, which may create more data traffic and collisions. This type of failure can make the channel even busier by creating a lot of collisions. As a result, the effective throughput of the channel decreases.
If the joining node is able to determine that the network is busy, instead of back-to-back retries, the joining node can wait for a predetermined period to allow the network to settle. If the success likelihood of an attempt is too low, then it is better to not even try to communicate. The added communication of the attempt increases the network load without producing any benefit and while disrupting the communication of other nodes.